1. Technical Field
The present invention relates to electrical plugs, and more particularly, to a three-pin electrical plug with improved terminal structure, wherein the plug, in virtue of the structural improvement in its terminals, is conductive to mass manufacturing in terms of both efficiency and cost.
2. Description of Related Art
A three-pin electrical plug features an earth pin for connecting the ground for safety in addition to its two conductive blades, also known as terminals.
Referring to FIGS. 1 through 3, for making a conventional three-pin electrical plug, two terminals 91 and an earth pin 93 have to be pre-made and arranged on a plug body 95. For making the terminal 91, a plurality of preforms 91′ is formed in batch. Each of the preform 91′ has a blade portion 911, a joint portion 912 and a wire-gripping portion 913. Traditionally, as shown clearly in FIG. 2, the preform 91′ is symmetrical about its lengthwise central axis A9 (a line through centers of the blade portion 911, the joint portion 912 and the wire-gripping portion 913). In other words, basing on the axis A9, both the blade portion 911 and the wire-gripping portion 913 have two halves thereof equally extended to the same width, namely W91 being equal to W92 while W93 is equal to W94. Preforms 91′ such made are then separated and twisted into a terminal 91 to be arranged on the plug body 95 together with the earth pin 93 and another said terminal 91, as shown in FIG. 3. As can be seen in FIGS. 3 and 4, the terminal 91 at this time has its wire-gripping portion 913 shaped into a U-like shaped with its two halves lifted symmetrically.
Referring to FIG. 5, the plug body 95 carrying the terminals 91 and the earth pin 93 is then subjected to a wire-fixing process where a pressing mold 80 with dies 81, 83 is used to deform the wire-gripping portions of the earth pin 93 and terminals 91 so as to affix conductive wires 85 thereon. For fitting the terminals 91 arranged as described above, the first dies 81 flanking the second die 83 have a shortest distance therebetween much shorter than the shortest distance between the axes (i.e. the blade portions 911 of the terminals 91) of the two conductive wires 85 corresponding thereto. Consequently, in the confined mold 80, side walls 811 of the first dies 81 bordering the second die 83 are necessarily thin, and this being a major problem to the prior art. That is, the thin side walls 811 of the first dies 81 tend to break over the repeated pressing operation.
Since either repair or replacement of the dies or the mold is costly, there is a need to develop a scheme that is conductive to mass manufacturing of a three-pin electrical plug in terms of both efficiency and cost without changing the relative position of its earth pin and terminals so that the improved three-pin electrical plug is still compatible to existing power outlets.